This invention relates to inflatable emergency evacuation slides used primarily on aircraft, off-shore drilling platforms and the like. More particularly this invention relates to delayed restraint release devices and redundant systems used in conjunction with the deployment of such slides.
In the case of off-shore drilling platform break-ups, aircraft crash landings or other aircraft emergencies away from airport terminal building, it is normally desirable to evacuate the passengers and cargo as quickly as possible. Emergency evacuation slides have long been provided on most aircraft and drilling platforms for this purpose. Further discussion herein of the present invention will be generally directed to aircraft applications. It should be understood, however, that the present invention has equal applicability to many other analogous fields such as off-shore drilling platforms and the like.
Presently, the most common type of evacuation slide in use takes the form of an inflatable ramp which is stored in the aircraft adjacent an exit door in its deflated condition. In emergencies, the deflated slide is extended from the aircraft. Only then is it inflated. When the slide is extended from the aircraft it hangs in a relatively limp position. In this position it is highly vulnerable to wind deflections which often occur when a cross wind blows toward or across the evacuation exit. Under such circumstances the limp slide may be blown underneath the aircraft or elsewhere, making it completely useless when inflated. For further discussion of this problem, see U.S. Pat. No. 3,018,867 issued to Heyniger.
To eliminate the problems created by wind deflection, devices have been used to restrain the full extension of the slide until it is partially inflated to a predetermined degree. In many such devices an area of the slide adjacent its lower end is temporarily and releasably secured to an area adjacent its upper end or to the aircraft itself until a suitable inflation pressure is obtained. At such time the temporary securement permits the release and separation of the lower end from the upper end of the slide. Upon such release of the lower end of the slide, the continuing inflation pressure forces the lower end to first swing outwardly from the aircraft and then downwardly to the ground. Further discussion of the mechanism can be found in U.S. Pat. No. 3,391,771 issued to Day.
Preferably the temporary and releasable restraint release device used to secure the lower end of the slide is self releasing upon a predetermined partial extension of the slide from the aircraft. The self releasing characteristic of the restraint device eliminates human error due to lack of skill or panic as might well occur in emergency situations where the present invention is intended to be utilized.
It is preferable that the restraint device be released at a predetermined and precise inflation pressure which will normally correspond to a predetermined and precise orientation of the partially inflated slide. Deviation from this pressure can render the slide useless. Release of an uninflated or underinflated slide may cause wind deflection problems as heretofore referred to, resulting in disaster. On the other hand, undue delay in fully extending the slide similarly can be disasterous in a situation where time is of the essence.
It should also be understood that a restraint device, set to release at an inflation pressure which is too low, is inadequate since it will prematurely free the lower end of the slide and render it susceptible to wind deflections. A restraint device, set to release at too high of a pressure, is likewise, inadequate since such pressure may never be attained and will also render its slide useless.
One such type releaseable restraint device which achieves the desired objectives as set forth above and overcomes such disadvantages is described in U.S. Pat. No. 3,944,023 to Fisher. According to the disclosure of the patent, an emergency evacuation slide is precluded from full extension by the presence of a strap, separable by a shear pin, breakable only upon the attainment of a predetermined pressure in the slide. Such a releaseable restraint normally comprises two meeting components coupled by a shear pin or pins with a cover to protect the pins and protect tampering with the pins prior to use. Tension due to the inflation pressure within the slide is transmitted to the restraint device and shear pins by means of two straps, each of which couples an end of the component with a segment of the slide. Only when the pressure within the slide reaches a predetermined pressure limit will the shear pin break and release the slide to permit its full extension to the position for proper utilization.
Certain recently developed escape slides, such as those for the Boeing 747 stretch upper deck aircraft, are designed with two inflatable chambers and two associated inflation devices. Such slides are required to inflate and be utilized with only one chamber functioning. This condition requires an improved delayed type release mechanism since complications may arise when such prior art types of restraint devices are employed in an inflatable emergency evacuation slide composed of two fluidly independent inflatable chambers. Such type of emergency evacuation slide is employed for example in the stretch upper deck of the Boeing 747 aircraft and is described in U.S. Pat. No. 4,434,870, issued in the name of John M. Fisher. Such complications would occur if the pneumatic inflation mechanism for only one of the inflatable chambers were actuated while the other inflation mechanism remained unactuated or if the tubing in one of the chambers were to rip to preclude its inflation.
In a situation where the lower chamber would inflate, insufficient pressure build-up would occur to break the shear pin or pins of the primary emergency restraint release device of the aforementioned U.S. Pat. No. 3,944,023. If such a situation were to occur, a secondary or back-up delayed restraint device would have to be utilized to insure deployment of the slide even though the upper chamber were not to become inflated. Such back-up delayed restraint release device may be used, not only in a back-up mode, but also, if desired, as a primary releaseable restraint device, independent of other devices. In such a situation it would consitute the sole delayed restraint release device in its inflatable emergency evacuation slides. Such a system is disclosed in U.S. patent application Ser. No. 443,425, filed Nov. 22, 1982 now U.S. Pat. No. 4,460,062. Such devices, however, require the use of additional inflatable mechanisms on the slide for extension of a lanyard to constitute the delayed restraint feature operable in either a back-up or primary mode.
Another situation in which improved delayed restraint release devices are employed are in those situations wherein the primary device receives a sharp or large load prematurely, prior to the precise pressure being applied to the device through the inflatable members. When this occurs, the delayed restraint release device may be activated to release the slide prior to the predetermined time. In such situations it may be desirable to have a back-up member to further hold the inflatable slide in its semi-collapsed orientation until the the proper pressure is received on the back-up delayed restraint release device to only then permit deployment of the slide assembly.